Gauge fields and quantum theory

This thesis investigates the problems within quantum mechanics for the Bohm model caused by Lorentz invariance and the existence of photons. A model describing the electromagnetic interactions of fermions is produced which does not use photons and avoids these problems. It is then shown how these techniques can be extended to linearised gravitational interactions. Finally semi-classical gravity and the possibility of gravitationally induced collapse are considered. In the first part of the thesis two modifications to the Bohm model are proposed. One takes account of Lorentz invariance, and the other is capable of describing photons. The main part of the thesis is devoted to describing interactions in a way which does not need extra gauge particles, and so is in the same spirit as the Bohm model. Electromagnetic interactions are formed using a 4-potential operator which is calculated directly, without imposing commutation relations on the 4-potential. This leads to an expression for the 4-potential in terms of the Dirac field, and results in there being no photon states. There are various ways of constructing the theory and the scattering matrix of standard QED is compared to the scattering matrix of the version which appears to be most similar. Considering only the matrix elements between fermion states, they are found to be in agreement at the order e(^2), but disagree at the order e(^4). It follows that this model, which otherwise appears to be a self consistent theory of QED, cannot agree with experiment. The same techniques can be used to quantise General Relativity when it is linearised about the Minkowski metric. The metric operator is calculated in terms of the Dirac field. The interaction is similar to that of electrodynamics, being of order 4 in the Dirac field. Finally issues relating to gravitational collapse are discussed

A combined deficiency of tissue factor and PAR-4 is associated with fatal pulmonary hemorrhage in mice

Mice with a complete absence of tissue factor (TF) die during embryonic development whereas mice with low levels of TF (Low-TF mice) survive to adulthood. Low-TF mice exhibit spontaneous hemorrhage in various organs, including the lung. In contrast, mice can survive without protease-activated receptor (PAR)-4, which is the major thrombin receptor on mouse platelets. We determined the effect of combining a deficiency PAR-4 (primary hemostasis) with a deficiency in TF (secondary hemostasis) on embryonic development and survival of adult mice

New insights into the mechanisms of venous thrombosis

Venous thrombosis is a leading cause of morbidity and mortality in industrialized countries, especially in the elderly. Many risk factors have been identified for venous thrombosis that alter blood flow, activate the endothelium, and increase blood coagulation. However, the precise mechanisms that trigger clotting in large veins have not been fully elucidated. The most common site for initiation of the thrombus appears to be the valve pocket sinus, due to its tendency to become hypoxic. Activation of endothelial cells by hypoxia or possibly inflammatory stimuli would lead to surface expression of adhesion receptors that facilitate the binding of circulating leukocytes and microvesicles. Subsequent activation of the leukocytes induces expression of the potent procoagulant protein tissue factor that triggers thrombosis. Understanding the mechanisms of venous thrombosis may lead to the development of new treatments

Triggers, targets and treatments for thrombosis

Thrombosis — localized clotting of the blood — can occur in the arterial or the venous circulation and has a major medical impact. Acute arterial thrombosis is the proximal cause of most cases of myocardial infarction (heart attack) and of about 80% of strokes, collectively the most common cause of death in the developed world. Venous thromboembolism is the third leading cause of cardiovascular-associated death. The pathogenic changes that occur in the blood vessel wall and in the blood itself resulting in thrombosis are not fully understood. Understanding these processes is crucial for developing safer and more effective antithrombotic drugs

Mental health in sport: the role of authentic leadership, competition level, and sport type

Introduction Mental health is an important part of an individual’s overall health. It is a complex topic and can be examined in terms of a combination of subjective wellbeing and mental illness. Factors can influence one’s mental health either positively or negatively, and these can be described as protective or risk factors. Authentic leadership is a leadership style has been related to positive outcomes in sport. Competition level has been shown to relate to mental health as elite athletes often demonstrate a greater prevalence of mental illness than others. Sport type is another factor that influences mental health as individual sports athletes often demonstrate greater levels of mental illness and lower wellbeing due to a lack of social nature compared to team sports. The purposes of this study were to identify the relationship between authentic leadership and mental health, to identify whether competition level or sport type moderate the relationship between authentic leadership and mental health, and understand the process in which this relationship occurs. Method 647 athletes (n=281 female) from a variety of sports (n=194 individual sports athletes) and competition levels (n=104 elite) responded to a short online questionnaire measuring demographics, authentic leadership, psychological capital, teammate behaviours, subjective wellbeing, and mental illness. Athletes were recruited via social media platforms, through university lectures and emails, and local sports clubs and colleges. Amazon vouchers were offered as prizes as an incentive to increase response rate. Data was collected using Jisc Survey and analysed on IBM SPSS Statistics. Results Authentic leadership was positively correlated with subjective wellbeing and negatively correlated with mental illness. There were no significant differences across competition level on subjective wellbeing or mental illness. There was a difference in sport type on mental illness: individual athletes had higher scores on mental illness; but there was no significant difference for subjective wellbeing. Neither sport type nor competition level moderated the relationship between authentic leadership and subjective wellbeing or mental illness. Gender moderated the relationship between authentic leadership and mental illness, as authentic leadership was not related to a decrease in mental illness in females, but it was in males. Psychological capital partially mediated the relationship between authentic leadership and both subjective wellbeing and mental illness. Prosocial teammate behaviours partially mediated the relationship between authentic leadership and subjective wellbeing, and antisocial teammate behaviours did not mediate either relationship between authentic leadership and subjective wellbeing or mental illness

The many faces of tissue factor

Tissue factor (TF) is a member of the cytokine receptor superfamily and binds FVII/VIIa. The TF:FVIIa complex has both procoagulant and signaling activities. It functions in many biological processes, including hemostasis, thrombosis, inflammation, angiogenesis and tumor growth. Importantly, TF is essential for hemostasis. However, increased TF expression within atherosclerotic plaques and elevated levels of circulating TF-positive micro particles promote thrombosis. TF increases inflammation by enhancing intravascular fibrin deposition, by increasing the formation of pro-inflammatory fragments of fibrin and by generating coagulation proteases, including FVIIa, FXa and thrombin, that activate protease-activated receptors (PARs). In endotoxemia and sepsis, TF-dependent thrombin generation and activation of PAR1 on dendritic cells enhance inflammation. Finally, the TF:FVIIa complex contributes to tumor growth by activating PAR2

The Role of Tissue Factor and Factor VIIa in Hemostasis

Tissue factor (TF) is a transmembrane receptor for Factor VII/VIIa (FVII/VIIa). It is constitutively expressed by cells surrounding blood vessels. The endothelium physically separates this potent “activator” from its circulating ligand FVII/FVIIa and prevents inappropriate activation of the clotting cascade. Breakage of the endothelial barrier leads to exposure of extravascular TF and rapid activation of the clotting cascade. TF is also expressed in certain tissues, such as the heart and brain, and provides additional hemostatic protection to these tissues. Small amounts of TF are also present in blood in the form of microparticles, which are small membrane vesicles derived from activated and apoptotic cells. Levels of microparticle TF increase in a variety of diseases, such as sepsis and cancer, and this so-called “blood-borne” TF may contribute to thrombosis associated with these diseases. Recombinant FVIIa has been developed as an effective hemostatic drug for the treatment of hemophilia patients with inhibitory antibodies. In addition, it is used for patients with bleeding that do not respond to conventional therapy. However, the mechanism by which recombinant FVIIa restores hemostasis has not been clearly defined. In conclusion, the TF:FVIIa complex is essential for hemostasis and recombinant FVIIa is an effective hemostatic drug

The Efficacy of the Eigenvector Approach to South African Sign Language Identification

Masters of ScienceThe communication barriers between deaf and hearing society mean that interaction between these communities is kept to a minimum. The South African Sign Language research group, Integration of Signed and Verbal Communication: South African Sign Language Recognition and Animation (SASL), at the University of the Western Cape aims to create technologies to bridge the communication gap. In this thesis we address the subject of whole hand gesture recognition. We demonstrate a method to identify South African Sign Language classifiers using an eigenvector approach. The classifiers researched within this thesis are based on those outlined by the Thibologa Sign Language Institute for SASL. Gesture recognition is achieved in real time. Utilising a pre-processing method for image registration we are able to increase the recognition rates for the eigenvector approach

Mental health in athletes:Does authentic leadership matter?

Recent research has attested to the prevalence of mental health issues in sport, and the need to identify factors that could promote athletes’ mental health. In this study, we investigated: (a) whether authentic leadership is associated with athletes’ mental health directly and indirectly via psychological capital and prosocial and antisocial behaviour experienced from one’s teammates; and (b) whether the hypothesized model testing these relationships is the same in higher versus lower competitive level athletes. We examined two dimensions of mental health, namely positive mental health and mental illness. A total of 751 athletes (Mage = 22.92, SD = 8.53; 294 female) from a range of sports completed a multi-section questionnaire administered via an online survey. Structural equation modelling showed that authentic leadership was positively related to positive mental health via psychological capital and prosocial behaviour and negatively linked to mental illness via psychological capital and antisocial behaviour. The effects of authentic leadership on positive mental health via prosocial teammate behaviour and subsequently psychological capital, and on mental illness via prosocial teammate behaviour, were stronger in higher compared to lower competitive level athletes. The findings suggest that by adopting an authentic leadership style coaches could strengthen athletes’ positive mental health and protect them from mental illness. This may happen by increasing athletes’ psychological capital and prosocial behaviour within the team and decreasing antisocial behaviour within the team